The ball screw mechanism is widely used as a feed screw, and is provided with a ball rolling passage defined by a thread groove formed around a screw shaft and a corresponding thread groove formed on the inner circumferential surface of a nut, and a plurality of balls (steel balls) that roll along the ball rolling passage. In such a ball screw mechanism, it is necessary to recirculate the balls in the ball rolling passage, and a deflector system using a deflector fitted into the nut is known as one of the systems for recirculating the balls. The deflector typically includes a tongue extending into the ball rolling passage for scooping up the balls from the ball rolling passage and a ball guide passage for guiding the balls scooped up by the tongue into a ball return passage formed in the nut.
The ball guide passage consists of a direction changing passage that bends in the shape of letter L to receive the balls from the tongue in the circumferential direction of the nut, and pass the balls to the ball return passage extending in the axial direction. Owing to this bent configuration, the deflector is typically formed by two pieces jointly defining the ball guide passage so that the molded products may be easily removed from the mold when manufacturing the deflector by casting metal or molding plastic material. (See Patent Documents 1 and 2, for example.) The deflector formed as an assembly of two pieces may be referred to as a multi-piece deflector.